Can I chain where clauses conditionally?

Question

I’m using Peewee as ORM extensively and within my DAO API layer I need to conditionally make a query narrower e.g.

query = UserModel.select().where(UserModel.last_name == last_name)
if first_name is not None:
   query = query.where(UserModel.first_name == first_name)

# ... more conditions then

df = pd.DataFrame(query.dicts())

is this the most idiomatic way to conditionally make the queries narrower in Peewee or is there another way? Are there any pros and cons of doing this?

Asked By: SkyWalker

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Source

Answer 1

I would suggest to doing first the dynamic condition and then calling where clause.

query = UserModel.select()
filtered = UserModel.last_name == last_name

if first_name is not None:
   filtered &= UserModel.first_name == first_name
   
# ... more conditions then

# if some_cond:
#    filtered &= some_other_cond

# if some_cond:
#    filtered |= some_other_cond
 
# put one or other depending on
# the logic of your function 

query = query.where(filtered)

df = pd.DataFrame(query.dicts())

Edit : fix an error in the code

Answered By: PXP9

Answer 2

Sure you can do this a couple ways:

# Chaining calls to .where() will AND the clauses together.
q = q.where(Model.field == 'something')
q = q.where(Model.other == 'another')

# Another option:
accum = []
accum.append(Model.field == 'something')
accum.append(Model.other == 'another')
q = q.where(*accum)

# Or you can explicitly AND them together:
q = q.where(reduce(operator.and_, accum))

Etc.

Answered By: coleifer

Can I chain where clauses conditionally?

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